1. Field of the Invention
The present disclosure generally relates to III-nitride and, more particularly, to III-nitride having indium nitride microdisks.
2. Description of the Related Art
For the conventional light-emitting diodes (LEDs), there are two approaches to generate white light with GaN-based material. In the first approach, the blue light generated by indium gallium nitride can be mixed with yellow-light (Ce-doped yttrium aluminum garnet, YAG, which is its complementary color) phosphor to generate white light. In the second approach, the InxGa1-xN/GaN red-light, green-light and blue-light LEDs can respectively emit monochromatic lights to be mixed with each other to generate white light.
The first approach is currently the mainstream of the light-emitting technology. However, it has some disadvantages. First, the first approach falls within the scope of the patent owned by S. Nakamura. Secondly, it is difficult to acquire the rare-earth elements such as yellow-light (Eu-doped), red-light (Er-doped) and green-light (Tm-doped) phosphors. Third, the yellow light is generated from the blue light generated by the indium gallium nitride. Namely, the energy of the blue light is partially absorbed by the phosphor (Ce-doped YAG) and converted into the yellow light. The conversion process causes the loss of the energy and reduces the light-emitting efficiency. The loss of the energy occurs in the form of thermal radiation, which makes the device fragile and shortens the service life of the device.
The easiest way to overcome the above problem would be to adopt the second approach which does not require the phosphor. However, the semiconductor physics suggests that the lattice mismatch between indium nitride and gallium nitride along the “a” axis is as high as 10.9%. Thus, it is difficult to grow high indium content of InxGa1-xN/GaN quantum wells on the GaN microdisks. In addition, the GaN microdisk usually has a thickness of 2 μm which is larger than required. Therefore, it would be needed to cut the bottom part of the microdisk, leading to a complex production process. Furthermore, most of the researches regarding the 3D InN are directed to nanowires or nanopillars. The diameter of the nanowire or nanopillar is usually 70 nm only and includes an acute tail end (non-planar form). Thus, it is not suitable for growing the InxGa1-xN/GaN quantum wells. Although the acute tail end can be shaped into a planar form, the size is still too small to be used in the modern production process.
Thus, it is necessary to improve the conventional epitaxial structure.